In particular, yet not restrictive manner, the invention concerns a mechanical locking system for rectangular floor panels with long and short edges. It should be emphasized that long and short edges are only used to simplify the description. The panels could also be square. However, the invention is as well applicable to building panels in general. More particularly the invention relates to the type of mechanically locking systems, which allow that all four edges of a panel could be locked to other panels by an angling action. The long and short edges have a mechanical locking system, which could be locked horizontally with a strip and a locking element on one edge that cooperates with a locking groove in another edge and vertically with a tongue in one of the edges that cooperates with a tongue groove in the other adjacent edge. The long edges could be locked with angling and the short edges with a combined vertical and horizontal snap action. The short edges locking system is preferably formed in one piece of a wood fibre or a plant fibre based material or a plastic material that is a part of the panel core. The locking system could also be formed of a preferably separate wood fibre based material, which is connected to the panel, preferably as an edge section, and glued to an upper and lower layer of the floor panel and formed by machining.
Floor panels with locking systems of this kind are described in for example WO 01/02669 (Akzenta), WO 01/51732, (Hulsta-Werke), WO 01/75247 (Perstorp Flooring), WO 01/77461 (Välinge) and WO 2001/088306 (Kronospan). The floor panels have a locking system comprising a locking element cooperating with a locking groove, for horizontal locking, and a very small tongue, which cooperates with a tongue groove, for vertical locking. The locking systems are designed such that fibres could be compressed and/or the strip could bend downwards during connection of two adjacent edges. Such locking system could be used to connect two adjacent short edges vertically and horizontally by a combined vertical and horizontal displacement. One edge could be pressed downwards vertically until the tip of the small tongue reaches the opening of the tongue groove. The small tongue is thereafter automatically pushed mainly horizontally into the tongue groove by the compressed fibres and/or by the strip and the locking element that snaps and springs back towards its initial position.
This type of vertical and horizontal snapping of the short edges is described as a locking system that could be combined with a long edges locking system that could be connected by angling. Long edge locking systems are shown which are mainly designed to lock the long edges such that they form a tight fit. Such long edge locking systems were originally used in combination with a horizontal snap system on the short edges. They were designed such that they could be displaced horizontally in order to lock the short edges with a horizontal snap action. The snapping is made with a hammer and a tapping block.
According to the known technology, a whole floor is intended to be installed with an angling action only where a long edge of a new “folding panel” is connected with angling to a first panel in a first row and where a short edge of this folding panel is connected with the same angling action by a vertical snap to a short edge of a second panel in a second row.
Such known locking systems, hereafter referred to as “vertical snap folding” systems have however not been successful on the market since they suffer from several major disadvantages as described below.
Displacement Friction
A vertical snap folding of this type requires a displacement of the folding panel along its long edge during the final stage of the folding action when the folding panel is angled down to the sub floor and when the short edges are connected by a combined vertical and horizontal snap action which is required to bring the small tongue into the tongue groove. There is a risk that the short edge locking system will not lock automatically since it is not able to overcome the friction between the long edges and to pull together the panels to the final locked position. The friction between the long edges is high mainly due to the geometry of the locking systems but also due to production tolerances, swelling, shrinking and bending of the panels. A gap between the short edges will in most cases remain after the folding and the panels must be displaced horizontally with a hammer and a tapping block along the locked long edges in order to finally lock the short edges. This make installation complicated and there is a great risk that the locking system could be damaged. It is not possible to use just a lose connection on the long side with low friction that could compensate for the swelling and bending since this will give a low quality locking system with for example open gaps and the locking system will not be able to prevent moisture and dirt to penetrate into the joint.
Small Tongue
The design of the short edge locking system is such that a tip of the tongue that is inserted into the tongue groove is made very small in order to allow vertical snapping without damaging parts of the locking system during the vertical pressing of the short edges. The contact surfaces between the upper part of the tongue and the tongue groove are therefore made very small and they are generally rounded or inclined in order to allow the insertion of the tongue into the groove. The vertical locking it not reliable and strong enough and an undesired unlocking could occur during swelling and shrinking of the installed floor or when a heavy load is applied on the floor surface.
Flexibility and Guiding
The design of the strip and the locking element is such that the flexibility of the strip and the vertical guiding of the locking element into the locking groove are not sufficient to guarantee a reliable and easy locking. The edges must be knocked together with a hammer and a tapping block or pressed very hard vertically against each other. Parts of the locking system are often damaged during such installations.
The inventor has discovered that such installation problems often occur when the panels are thin, for example 6-9 mm and have a width of more than 100 mm, for example 100-300 mm. Such panels are very flexible and the long edges are not able to support the middle parts of the short edges and keep them in a vertically locked position. The small tongue could snap out vertically when people walk on the floor. The vertical snap resistance during installation is considerable. Some panels are especially difficult to handle for example long panels, panels with compact locking systems or with locking systems locked with pre tension and panels comprising core materials with rough fibre structures. All such panels could be very difficult to displace in locked position along the long edges and they are in principle not possible to lock with a vertical snap action without major problems.
In order to overcome these problems locking systems have been developed that do not require a displacement of a panel during vertical locking. Such displacement is replaced by a displacement of a flexible tongue. Such flexible tongue locking systems, for example as described in WO 2006/043893 (Vätinge), comprise a separate flexible tongue with a protruding part that could be displaced horizontally during locking. A panel with a flexible and displaceable tongue is very easy to lock vertically without the use of a hammer and a tapping block and solves all the above-mentioned problems. The disadvantage of such systems is that a separate tongue has to be produced and inserted into a panel edge during production.
A vertical snap folding system which requires a displacement of a panel during the final stage of the locking could however be competitive against the flexible tongue systems if the above mentioned disadvantages could be eliminated since it is very easy and cost efficient to produce. The whole locking system could be formed in one piece with the core of the panel and no separate materials have to be produced with special tools and inserted into the short edge.
The invention aims to solve installation problems in flooring which is intended to be installed with a vertical snap folding system having a short edge locking system with a tongue formed in one piece with the panel core and where the short edge locking system requires a horizontal displacement of a panel that is locked with its long edge to an adjacent panel.